Green’s Dictionary of Slang

bobstick n.

[ety. unknown]

1. a shilling (5p).

[UK]Vaux Vocab. of the Flash Lang.
[UK]‘Jon Bee’ Dict. of the Turf, the Ring, the Chase, etc.
[UK]G. Kent Modern Flash Dict.
[UK]Flash Dict. in Sinks of London Laid Open.

2. thus, a shilling’s worth.

[UK]Grose Classical Dict. of the Vulgar Tongue ms. additions n.p.: Bob-Stick of Slim. A Shillings worth of Punch. Cant.
[UK]G. Parker Life’s Painter 137: I say, call for a bobstick of rum slim.
[UK]W.T. Moncrieff Tom and Jerry II v: Hang cards! bring me a bob-stick of rum slim or a glass of Barsac.